To add to this comment. Most of the questions and answers in stackoverflow stem from situations not covered by the documentation or when the documentation fails. LLMs don't have a way to learn about these issues and how to address them because they require actual implementations to assess/validate.

Its the same reason why git repositories would also fail to meet this need. Repositories only contain (typically working code) without much context on why changes were made or were needed. Technically githib issues or jira tickets could help cover the gaps of something like stackoverflow dissappearing, but would ultimately mean that the information could be locked behind paywalls or corporate systems.